1. Field of the Invention
The present invention relates to an ignition timing control device for an internal combustion engine in which two ignition plugs are disposed for each cylinder.
2. Description of the Related Art
Conventionally, an ignition timing control system, for example, as shown in Japanese Patent Unexamined Publication No. Hei. 6-323230, in which a plurality of ignition plugs are disposed for each cylinder of an internal combustion engine, and the ignition timings of the ignition plugs are made different from each other to improve exhaust emission characteristics is known. In this system, in order to reduce the load on a calculation unit in the case where the ignition timings of the plural ignition plugs are determined in accordance with the operation state of the engine. On the other hand, a calculation for determining normal ignition timing with respect to specific ignition plug(s) is performed, and, with respect to the other ignition plug(s), the ignition timing is determined by a relatively simple calculation expression in accordance with the ignition timing of the specific ignition plug(s).
In an internal combustion engine in which each cylinder has a plurality of ignition plugs, however, it is not always necessary to make ignition timings of the ignition plugs different from one another in all of operation states of the engine. From the viewpoint of reduction of the calculation load on the calculation unit, therefore, there is room for further improvement.
The invention has been conducted in view of the problem. It is an object of the invention to provide an ignition timing control device for an internal combustion engine in which two ignition plugs are disposed for each cylinder, can control more adequately ignition timings of the ignition plugs to reduce the load on a calculation unit, and effectively realize suppression of knocking and vibration noises.
In order to attain the object, according to a first aspect of the invention, an ignition timing control device for an internal combustion engine controls ignition timing of an internal combustion engine. Here, in the internal combustion engine, two ignition plugs that perform at least one igniting operation in one cycle are disposed on an diagonal line of a combustion chamber of each cylinder. The two ignition plugs ignite at different ignition timings in predetermined operating region which is determined on the basis of a rotational speed and load of the engine, and ignite at a same ignition timing in an operating region other than the predetermined operating region.
According to this configuration, in the predetermined operating region which is determined on the basis of the rotational speed and load of the engine, the two ignition plugs ignite at different ignition timings. While, in the operating region other than the predetermined operating region, the ignition plugs ignite at the same ignition timing. In this case, the predetermined operating region is restricted to a region where the effect of the setting of different ignition timings is remarkably achieved. Therefore, the load on a calculation unit and the memory capacity can be reduced. In the predetermined operating region, an excellent effect of suppressing knocking and vibration noises can be attained by the setting of different ignition timings.
The predetermined operating region is preferably set to an operating region where the engine rotational speed is in a region between predetermined upper and lower limits and the engine load is equal to or larger than a predetermined load. By the way, each of the cylinders of the engine can be divided into an intake side and an exhaust side by a plane that is substantially perpendicular to a direction along which an intake port connected to the combustion chamber of the cylinder elongates. Here, the plane contains a center line of the cylinder, preferably, the two ignition plugs are placed in the intake side and the exhaust side, respectively.